The present invention relates to an apparatus for controlling the movement of a piston wherein a double-action pneumatic piston-cylinder drive is provided, for example, for (mechanically actuating welding electrode holders for electrical resistance spot welding.
Generally speaking pneumatic devices of the type to which the invention pertains, are known, whereby a particular operating pressure acts on the piston movable being within a pneumatic cylinder, whereupon the electrodes of a dot welding device are moved toward each other within a particular welding cycle. As the electrodes hit the work piece a certain rebounding occurs on impact. Moroever, the impact produces noise generally but acts also as an parasitic load on the bearing of the various movable parts. This, in turn, leads to a premature wear of the electrodes, and may even result in deformation of the work pieces.
It is known for purposes of reducing the rebounding effect to provide a multi-stage pneumatic cylinder arrangement wherein the stages are telescoped in some fashion, they may be attenuated by means of air or oil. These two features for solving the problem, however, have the disadvantage that the cylinders and the pneumatic drive generally becomes quite expensive and often do not meet standardized specification requirements. Moreover, it is often necessary particularly in the latter case, to provide unique construction aspects separately in each instance.